1. Field of the Invention
The present invention relates to ultrasound imaging systems, and in particular to a system, method and software program for performing ultrasonic imaging by launching a broad beam (Fat TX) having a preselected spatial energy profile at a target and processing energy received from the target to determine image data representative of the target. Particularly, the present invention is directed to a medical ultrasound diagnostic system, method and software program that creates image data of a target using ultrasonic Fat TX and multiline receive (Multiline RX) imaging.
2. Description of Related Art
A variety of methods and systems are known for performing ultrasonic imaging. U.S. Pat. No. 6,277,073 to Bolorforosh et al., U.S. Pat. No. 6,172,939 to Cole et al. U.S. Pat. No. 5,276,654 to Mallart et al. and U.S. Pat. No. 4,644,795 to Augustine, all of which are hereby incorporated by reference in their entirety, describe various methods and devices for performing ultrasonic imaging.
Generally, when performing ultrasonic imaging, a transducer element, typically in the form of a piezoelectric crystal is placed in physical communication with a target (i.e., a patient) to be imaged. When excited by a pulse of electric current, the piezoelectric element emits a burst of ultrasonic waves over a particular frequency spectrum and at a particular intensity. These waves then propagate into the target to image a structure or structures at various depths in the target. As the wave travels through the target to the desired depth, the wave energy is partially absorbed and/or reflected by progressively deeper tissue layers in the target until all of the energy has either been absorbed or reflected. For medical imaging purposes, energy reflected by the target then travels back to the piezoelectric element that launched the wave and/or another piezoelectric element wherein the wave energy causes the piezoelectric element to generate an electrical signal, which is then processed to form image data. Many such cycles can occur within a single second.
Despite the high speed at which data may be acquired with state of the art ultrasonic imaging devices, it is still challenging to image three dimensional (3D) volumes. Ultrasonic sampling in three dimensions in real time requires that the energy reflected from many points within the volume be measured each time the volume is scanned. Given that the rate at which data can be acquired is finite, due to the finite speed of sound, 3D imaging places a strict limitation on the number of transmit/receive cycles available for sampling the region to be imaged. The same is true for high frame rate, large field-of-view two-dimensional (2D) applications. Thus it is greatly desired to find ways to obtain more data in a given period of time.
Generally, medical ultrasonic imaging devices use a plurality of piezoelectric elements arranged in a transducer head, as seen in U.S. Pat. No. 6,172,939 to Cole. Such devices can be used to xe2x80x9csteerxe2x80x9d transmit (TX) and receive (RX) beams to form an image. This is generally done by xe2x80x9cscanningxe2x80x9d a beam to sequentially insonify the entire volume to be imaged. Scanning typically involves sequentially launching a plurality of beams at the target across its volume over the course of a single xe2x80x9cframexe2x80x9d of scan lines. Each discrete transmit beam is formed by energizing all or a subset of the piezoelectric elements in the transducer head with suitably delayed and weighted pulse waveforms. Each discrete transmit beam is intended to insonify only a small portion of the volume to be imaged. A hundred or so beams need to be launched to create a single 2D frame and many thousand are required to make a 3D frame. Especially in the latter case, this takes a significant amount of time.
One solution to expedite the rate at which data can be acquired involves using a comparatively wide, flat transmit beam as described in U.S. Pat. No. 4,644,795 to Augustine so that multiple receive beams within the flat transmit beam can be usefully employed simultaneously. This technique is generally referred to as xe2x80x9cmultiline receive.xe2x80x9d The transmit beamformer of Augustine uses amplitude weighting (based specifically on Sinc functions) to xe2x80x9csquare upxe2x80x9d the transmit beams and insonify a large area. The same waveforms are transmitted on every channel, but the amplitudes differ (or the waveforms may be inverted). However, even at the transmit focal point, using this approach to control the shape of the energy profile across the target has its limitations. Since only amplitude weighting is being used to create the wavefront, the uniformity of insonification of the tissue, and the rejection of targets outside the intended boundaries of the transmit beam is limited.
Multiline RX is a relatively efficient use of transmit cycles because it allows one to obtain multiple receive lines for each transmit event. Likewise, discrete Multiline Transmission (xe2x80x9cMultiline TXxe2x80x9d) can be used to increase the rate at which data can be acquired. The basic premise of Multiline TX is to use parallel transmission paths to transmit discrete multiple beams along adjacent, but spatially distinct, paths as described in U.S. Pat. No. 6,172,939 to Cole et al. Multiple transmit beams are emitted from the device, which are launched into the target. Multiline RX is also employed to form parallel receive beams, as discussed above. B-Mode data, which is indicative of the amplitude of the received echoes, may be obtained and displayed (and/or stored) from the received multiline echoes as known in the art.
These concepts can be expanded to their logical conclusion. The ratio of discrete receive beams can be varied in proportion to the transmit beams to xe2x80x9cseexe2x80x9d more points in the target. In xe2x80x9c2xc3x97xe2x80x9d Multiline RX, a receive beam is placed on either side of the center of the transmit beam. In xe2x80x9c4xc3x97xe2x80x9d Multiline RX, 2 receive beams are located on either side of the transmit beam, and so on. With a two dimensional xe2x80x9c2Dxe2x80x9d array of piezoelectric elements, one can extend the multiline concept into the elevation direction by receiving beams from above and below as well as both sides of the transmit beam.
Such conventional methods and systems have permitted incremental improvements in ultrasonic imaging capability. However, there still exists a strong need to improve the overall performance of ultrasonic imaging systems. As evident from the related art, conventional methods often require that a plurality of transmit events occur before being able to form a complete image of a target.
Likewise, the flat TX beamformer described in U.S. Pat. No. 4,644,795 is limited in its flexibility due to only varying the relative amplitudes of signals transmitted on each channel without changing the overall shape of the waveform from channel to channel. This limits the degree to which the steepness of the xe2x80x9cskirtsxe2x80x9d of the transmitted beam can be increased. Ideally, a transmitted beam should have a xe2x80x9cboxcarxe2x80x9d shape instead of a trapezoidal shape.
There thus remains a need to optimize ultrasound imaging techniques in order to obtain as much data as possible and provide as much insight as possible regarding a subject being imaged.
The purpose and advantages of the present invention will be set forth in and apparent from the description that follows, as well as will be learned by practice of the invention. Additional advantages of the invention will be realized and attained by the methods and systems particularly pointed out in the written description and claims hereof, as well as from the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the invention includes a system for performing ultrasonic fat beam transmission and multiline receive imaging, wherein the system comprises a transmitter configured to launch an ultrasound beam toward a target, wherein the beam has a predetermined spatial energy profile in at least one location in the target. The transmitter further includes a plurality of transducer elements wherein each transducer element is capable of converting a selected electrical waveform having a desired shape to produce an ultrasonic pressure wave. The system also includes a transmitter processor that is configured to generate the electrical waveform and control its shape (and time delay) on each channel connected to a transducer element such that the spatial energy profile of the ultrasound beam is controlled by controlling the shape of the waveform that is produced on each transducer element. The system also includes a receiver that receives energy from the ultrasound beam directed toward the target from the transmitter. Further, a receiver processor is provided that is configured to process the received energy to determine image data representative of the target.
Preferably, a system is provided wherein the spatial energy profile of the ultrasound beam is substantially flat at the location in the target and the receiver can be formed from at least a portion of the plurality of transducer elements as the transmitter and the final shape of the waveform launched from any transducer element is determined by combining at least two preselected waveforms. For example, more transducer elements can be used by a receive beam than by a transmit beam. Likewise, the transmitter and receiver can be formed of entirely different transducer elements, or using only some of the same transducer elements.
In another aspect of the invention a system is provided wherein the received energy is received in the form of at least one received beam having an outer periphery and the transmitter is further configured to send ultrasound guard beams on the outer periphery of the at least one received beam.
In yet another aspect of the invention a system is provided wherein the transducer elements are arranged in a substantially two-dimensional array and wherein the instantaneous frequency (and/or amplitude) of a waveform transmitted from a first transducer element can be different from the instantaneous frequency of a waveform transmitted from a second transducer element. The system allows for time delays on different channels to permit steering and focusing of the transmit and receive beams.
The invention also includes a method for performing ultrasonic Fat TX, Multiline RX imaging comprising the step of selecting waveforms to transmit on a plurality of transducer elements toward a target, wherein each transducer element is capable of producing a selected waveform having a desired shape and said transducer elements comprise a transmitter. The method also comprises transmitting an ultrasound beam from the transmitter, wherein the beam has a predetermined spatial energy profile in at least one location in the target. In this method, the spatial energy profile of the beam is controlled by controlling the shape of the waveform produced by each transducer element. The method also comprises receiving energy from the ultrasound beam directed toward the target from the transmitter and processing the received energy to determine image data representative of the target.
Preferably, a method is provided wherein the spatial energy profile of the ultrasound beam is substantially flat at the location in the target and the receiver is formed from the same plurality of transducer elements as the transmitter and the final shape of the waveform launched from any transducer element is determined by combining at least two preselected waveforms.
In another aspect of the invention a method is provided for forming an ultrasound beam wherein received energy is received in the form of at least one received beam having an outer periphery and the transmitter is further configured to send ultrasound guard beams on the outer periphery of the at least one received beam.
The invention also includes a machine readable program containing instructions for controlling a system to perform ultrasonic Fat TX, Multiline RX imaging, wherein the system has a transmitter, a transmitter processor, a receiver and a receiver processor, and the program comprises means for controlling transmission of an ultrasound beam from a plurality of transducer elements toward a target. The transmitted beam has a predetermined spatial energy profile in at least one location in the target wherein each transducer element is capable of producing a selected waveform having a desired shape, and the spatial energy profile of the beam is controlled by controlling the shape of the waveform produced by each transducer element.
Preferably, a machine readable program is provided containing instructions for controlling a system to perform ultrasonic Fat TX, Multiline RX imaging wherein the spatial energy profile of the ultrasound beam is substantially flat at least one location in a target and the final shape of the waveform launched from any transducer element is determined by combining at least two preselected waveforms.
In another aspect of the invention a machine readable program is provided wherein the received energy is received in the form of at least one received beam having an outer periphery and the transmitter is further configured to send ultrasound guard beams on the outer periphery of the at least one received beam.
In yet another aspect of the invention a machine readable program is provided wherein the instantaneous frequency of a waveform transmitted from a first transducer element can be different from the instantaneous frequency of a waveform transmitted from a second transducer element.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention claimed.